Engagement head for tensioning assembly

ABSTRACT

An engagement head for a rock bolt tensioning assembly is disclosed that is profiled to include at least one key surface to inhibit rotation of the engagement head relative to a rock surface, either by direct engagement with the rock surface or through abutment with a plate-like member that is engageable with the rock surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to rock bolting and in particular totension assemblies for rock bolts suitable for use in the mining andtunneling industry to provide rock and wall support. The invention issuitable for use in hard rock applications as well as in softer strata,such as that often found in coal mines, and it is to be appreciated thatthe term “rock” as used in the specification is to be given a broadmeaning to cover both these applications.

2. Description of Related Art

Roof and wall support is vital in mining and tunnelling operations. Mineand tunnel walls and roofs consist of rock strata, which must bereinforced to prevent the possibility of collapse. Rock bolts, such asrigid shaft rock bolts and cable bolts are widely used for consolidatingthe rock strata.

In conventional strata support systems, a bore is drilled into the rockby a drill rod, which is then removed and a rock bolt is then installedin the drilled hole and secured in place typically using a resin orcement based grout. The rock bolt is tensioned which allowsconsolidation of the adjacent strata by placing that strata incompression.

To allow the rock bolt to be tensioned, the end of the bolt may beanchored mechanically to the rock formation by engagement of anexpansion assembly on the end of bolt with the rock formation.Alternatively, the bolt may be adhesively bonded to the rock formationwith a resin bonding material inserted into the bore hole.Alternatively, a combination of mechanical anchoring and resin bondingcan be employed by using both an expansion assembly and resin bondingmaterial.

When resin bonding material is used, it penetrates the surrounding rockformation to adhesively unite the rock strata and to hold firmly therock bolt within the bore hole. Resin is typically inserted into thebore hole in the form of a two component plastic cartridge having onecomponent containing a curable resin composition and another componentcontaining a curing agent (catalyst). The two component resin cartridgeis inserted into the blind end of the bore hole and the mine rock boltis inserted into the bore hole such that the end of the mine rock boltruptures the two component resin cartridge. Upon rotation of the minerock bolt about its longitudinal axis, the compartments within the resincartridge are shredded and the components are mixed. The resin mixturefills the annular area between the bore hole wall and the shaft of themine rock bolt. The mixed resin cures and binds the mine rock bolt tothe surrounding rock.

Tension assemblies have been proposed to provide tension along rockbolts, for example cable bolts, which in turn provides a compressiveforce on the substrate, usually a mine shaft roof substrate, about thebolt.

SUMMARY OF THE INVENTION

Disclosed is a tensioning assembly for a rock bolt, the tensioningassembly comprising an engagement head that in use is forced into eitherdirect or indirect engagement with a rock surface, wherein theengagement head is profiled to include at least one key surface toinhibit rotation of the engagement head relative to the rock surface.

In one form the engagement head is arranged to engage the rock surfacethrough abutment with a plate-like member and rotation of the engagementhead relative to the plate-like member is inhibited by the at least onekey surface.

The positive engagement between the engagement head of the tensioningassembly and the rock surface, either directly or indirectly, acts toinhibit rotation of the engagement head and therefore may be used as ameans to inhibit twisting of the rock bolt shaft which places tension onthe shaft during tensioning. This is particularly useful in a cable boltapplication where twisting of the cable induces unwinding of the cablestrands. In some forms, the key surfaces are shaped to allow the shaftto be tilted with respect to the rock surface or plate-like memberwithout disengaging the head thus maintaining the engagement to inhibitrotation.

In one form the key surface is part of a projection that is formed onthe engagement head. In one form the key surface comprises radiallyprojecting lateral surfaces. In one form the lateral surfaces projectradially from a central zone to the circumference of the head. In oneform the key surface is located on a projection extending outwardly fromthe circumference of the head. In one form the key surface is located ina slot extending into the head. In one form the key surface is formed asone or more flattened surfaces formed as the engagement head.

In one form, the engagement head forms part of a bearer memberincorporating a passage through which the rock bolt extends. In aparticular form, the bearer member includes an inner surface thatdefines the passage and which incorporates a surface that cooperateswith an abutment mounted to, or formed in, the rock bolt to provide apositive engagement therebetween that inhibits rotation of the bearermember relative to the abutment about the bolt in at least onedirection.

In a second aspect, there is disclosed a combination comprising atensioning assembly according to any form described above and aplate-like member arranged to directly engage the rock surface, theplate like member including at least one plate key surface thatcooperates with the at least one key surface of the engagement head toinhibit rotation therebetween.

In a third aspect, disclosed is an engagement head for a tensioningassembly for a rock bolt, the engagement head being for direct orindirect engagement with a rock surface, the engagement head beingprofiled to include at least one key surface to inhibit rotation of theengagement head relative to the rock surface.

In one form the key surface of the engagement head is otherwise asdescribed above with respect to the tension assembly.

In a fourth aspect, disclosed is an engagement assembly for engagementbetween a rock surface and a tensioning assembly, the engagementassembly comprising a plate-like member arranged to directly engage therock surface, the plate like member including at least one plate keysurface and, a bearer member arranged to engage the tensioning assembly,the bearer member having a head including at least one head key surface,wherein the head key surface and the plate key surface are adapted toengage such that rotation of the head relative to the rock surface isinhibited.

In a fifth aspect, the invention is directed to a plate-like member foruse with the tension assembly or forming part of the engagement assemblyas described above.

In a sixth aspect, disclosed is a rock bolt assembly comprising a rockbolt having an axis, a bearer member for facing and urging against rockstrata, the rock bolt being arranged to extend through the bearermember, and an abutment mounted to, or formed in the rock bolt, theabutment and the bearer member incorporating cooperating surfaces thatprovide positive engagement therebetween that inhibits rotation of thebearer member relative to the abutment about the bolt axis in a leastone direction.

In yet a further aspect, disclosed is a method of inhibiting rotation ofa tensioning assembly with respect to a rock surface, the tensioningassembly including a bearer member, the method comprising positioning aplate-like member in contact with the rock surface; positioning a bearermember in contact with the plate like member; and causing a key surfacein the bearer member to abut a corresponding key surface in theplate-like member.

BRIEF DESCRIPTION OF THE DRAWING(S)

Embodiments will now be described by way of example only, with referenceto the accompanying drawings in which:

FIG. 1 is a perspective view of one embodiment of the tensioning devicedisposed on a cable bolt;

FIG. 2 is an exploded view of the tensioning device of FIG. 1;

FIG. 3 is a perspective view of the base member of a tensioning deviceof FIG. 1;

FIG. 4 is a cross-sectional view of the base member of FIG. 3;

FIG. 5 is a top view of the base member of FIG. 3;

FIG. 6 is a perspective view of the bearer member of a tensioning deviceof FIG. 1;

FIG. 7 is a cross-sectional view of the member of FIG. 6;

FIG. 8 is a top view of the member of FIG. 6;

FIG. 9 is a side elevation of the tensioning device of FIG. 1 connectedto a bearing plate and cable bolt;

FIG. 10 is cross-sectional view of the device of the assembly of FIG. 9;

FIGS. 11A to C show a perspective view from above, a plan view and across-sectional elevation of an alternative bearer member;

FIGS. 12A and B show a plan view and a cross-sectional side view of abearing plate for use with the bearer member of FIG. 11;

FIGS. 13A to C show a perspective view from below, a view from below anda side view of a bearing plate of a cable bolt tensioning assembly inaccordance with a further embodiment;

FIGS. 14A, B and C show a perspective view from below, a view from belowand a sectional view of a bearer member of a cable bolt tensioningassembly for use with the bearing plate of FIG. 13;

FIGS. 15A and B illustrate operation of the bearer member of FIG. 13with the bearing plate of FIG. 14;

FIGS. 16A, B and C show a perspective view from below, a view from belowand a side view of a bearing plate for a cable bolt tensioning assemblyin accordance with a further embodiment;

FIGS. 17A, B and C show a perspective view from below, a view frombelow, and a sectional view of a bearer member head for a cable bolttensioning assembly in accordance with a further embodiment for use withthe bearing plate of FIG. 16;

FIGS. 18A and B illustrate operation of the bearer member of FIG. 17with the bearing plate of FIG. 16;

FIGS. 19A and B show a view from above and a side view of a bearermember head for a cable bolt tensioning assembly in accordance with yeta further embodiment;

FIGS. 20A and B show a view from the side and a view from below of abearing plate for use with the bearer member of FIGS. 19A and B;

FIGS. 21A and B show a view from above and a side view of a bearermember head for a cable bolt tensioning assembly in accordance with yeta further embodiment;

FIGS. 22A and B show a side view and a view from below of a bearingplate for use with the bearing member of FIGS. 21A and 21B;

FIG. 23 shows a cross-sectional elevation of a tensioning assemblyaccording to yet a further form;

FIG. 24 is a perspective view from below of the actuator of a tensioningdevice of FIG. 1;

FIG. 25 is a cross-sectional elevation of the actuator of FIG. 24;

FIG. 26 is a detailed view to an enlarged scale of the end engagementprofile of the actuator of FIG. 24; and

FIGS. 27 to 36 are installation sequences (showing assembly sideelevations and cross-sectional views) for installing the tensioningdevice of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The following description relates to engagement heads for tensioningassemblies as best shown in FIGS. 11 to 22 for tensioning rock boltshafts that have been installed in a bore in rock strata and anchored tothe rock strata typically by a chemical and/or mechanical anchoringprocess. The description further relates to assemblies (best seen inFIGS. 1 to 10 and 23 to 26) for tensioning cable bolts and toinstallation procedures (shown in FIGS. 27 to 36) which utilize thedescribed engagement heads.

Tensioning Assembly

Referring firstly to the FIGS. 1 to 10, a first embodiment of atensioning assembly 1 is shown. The tensioning assembly 1 is for usewith a rock bolt 2 having a shaft 3 typically formed from wire strandsthat are bundled together. In use, the rock bolt is installed in a bore501 (see FIG. 27) formed in the rock strata 500 with a distal end (notshown) of the bolt 2 being disposed adjacent the blind end of the bore501 and a proximal end portion 3 b arranged to project from the bore501. The tensioning assembly 1 is arranged to be fitted onto thatproximal end portion 3 b so that it is disposed at an exterior surface502 of the rock strata.

The tensioning assembly comprises three primary components; a basemember 5 which is fixed to the shaft 3, a bearer member 10 which ismovable relative to the base member along the shaft and which isarranged to abut either directly or indirectly the rock strata 500, andan actuator 16 that is engageable with both the bearer member and thebase member and operative to transmit a biasing force to move the bearermember away from the base member which in use provides tensioning to thecable as will be described in more detail below.

In the illustrated form, the base member 5 comprises a first part thatforms a barrel 7, a second part that fauns a stem 8, and tension wedges6 which are located within the barrel 7 which in use secure the basemember 5 with respect to the shaft 3. The tension wedges 6 have an innerwedge face 6 a for defining a cable receiving passage for receiving thecable 2 and an outer wedge face 6 b, opposite the inner wedge face. Theouter wedge face has a profile complementary to the interior of thebarrel 7. The tension wedges 6 are forced into engagement with the cableunder loading of the barrel in the direction of the cable proximal end 3b. Further the barrel 7 and wedges 6 have sufficient strength to preventshear stress failure to ensure that the cable 2 is held in place by thetension wedges 6 within the barrel 7 under this loading.

The stem 8 of the base member 5 extends from the barrel 7 and along thecable 3. The stem 8 is cylindrical and merges with the barrel to form anannular shoulder 31 that in use faces towards the distal end of the rockbolt 2. An interior passage 32 is provided to allow the cable shaft 3 tobe inserted through the stem and the stem has a non-circular exteriorsurface 33 that includes key surfaces 9 which as shown are formed asflats on the exterior 33 of the stem 8.

The bearer member 10 is mounted on, and moveable with respect to, thestem portion 8. As best seen in FIGS. 6 to 8, the bearer member 10comprises an externally threaded body 11 and a dome head 13 at one endof the body. The body 11 has an internal cavity 34, the walls 35 ofwhich are complementary to the exterior 33 of the stem 8 and includeinternal keyed sections 12. The internal keyed sections 12 are locatedwithin the cavity such that when the bearer member 10 locates over thebase member 5 (such that stem 8 extends into the cavity in bearer member10), the external keyed sections 9 on the stem 8 engage with theinternal keyed sections 12 on the bearer member 10 thereby inhibitingthe rotation of the bearer member 10 with respect to the base member 12about the longitudinal axis of the shaft 3. However, the bearer member10 is movable along the stem 8 in the direction of the axis of thecable.

The bearer member 10 is arranged so that the dome head 13 engagesdirectly or indirectly with the rock surface into which the rock boltextends. The head 13 which incorporates an opening 35 to allow passageof the cable shaft 3 through the bearer member, may be shaped other thana dome (for example being flattened to form a plate like appearance) sothat it is engageable directly with the rock surface. However, in theillustrated forms, the dome head 13 is arranged to engage a separaterock bolt bearer plate 30 (see FIGS. 9 and 10) which in use ispositioned between the rock surface and the bearer member 10.

The dome head 13 shown in FIGS. 1 to 10 is hemispherical and engageswith an inner edge 36 of the plate 30 (as best shown in FIG. 10) formedon a boss 42 of the plate 30. This direct contact is arranged to providefrictional resistance so that in tensioning of the device 1 theengagement between the plate 30 and the head 13 inhibits rotation of thehead relative to the plate 30. Further the use of a generallyhemispherical head 30 allows the head to remain engaged (and therebyprovide the rotational resistance) with the plate 30 when the bearermember 10 is tilted at an angle with respect to the bearing plate 30,allowing for the axis of the rock bolt to be tilted with respect to thebearing plate 30, which may occur in use. As will be explained in moredetail below, the inhibiting of the rotation of the bearer memberassists in preventing twisting of the cable during tensioning.

FIGS. 11 to 22 disclose embodiments of the tensioning device where,rather than relying on frictional resistance between the head and theplate 30, a positive engagement arrangement is provided to inhibitrotation of the head 13 relative to the plate 30. In the illustratedform the head and plate have cooperating key surfaces to form thispositive engagement.

In the arrangement of FIGS. 11 and 12, the head 13 a is profiled toinclude key surfaces in the form of offset lateral surfaces 91. Thelateral surfaces 91 are angularly spaced apart about, and projectradially from, the head 13 a. The lateral surfaces are adapted to engagewith corresponding surfaces 92 in the bearing plate 30 a shown in FIGS.12A and 12B. In this way under clockwise rotation (looking from thelower end of the bearer 10) the surfaces 91, 92 are arranged to engageso as to provide positive engagement to inhibit rotation of the bearermember 10 with respect to the plate 30 a. Furthermore, the curvedsurfaces 91 a of the head 13 a behind the lateral surfaces 91 provide alead in surface for engagement of the head with the plate 30 a so thatthe head 13 a may be presented to the plate 30 a in any angularorientation about the axis of the bolt. The head can then engage theplate 30 a and on rotation of the head 13 a, the head 13 a will moveacross the plate 30 a until the complementary lateral surfaces 91 and 92engage. In the illustrated embodiment, the lateral surfaces 91 extendfrom the top of the “dome” of the head. This allows for the surfaces 91,92 to remain engaged when the bearer member 10 is tilted at an anglewith respect to the bearing plate 30 a, again allowing for the axis ofthe rock bolt to be tilted with respect to the bearing plate 30 a.

FIGS. 13 through 15 illustrate an embodiment where the head 13 b isprovided with a key projection 100 which forms a key surface which isarranged to interact with a corresponding slot 101 in the boss 42 b ofbearing plate 30 b. In operation the key projection 100 fits within theslot 101 and relative rotation between the bearing plate 30 b and bearermember 10 is prevented.

In the illustrated embodiment, the key projection 100 extends from thetop of the dome of the head 13 b to the lower end of the head. Thisallows for the key projection 100 to still engage with the slot 101 whenthe bearer member 10 is tilted at an angle with respect to the bearingplate 30 b.

FIGS. 15A and B illustrate how the bearer member head 13 b interactswith the bearing plate 30 b in operation, with the key 100 fitting intothe slot 101.

Note that in the drawings, only the dome head 13 b of the bearer member10 is shown. In FIG. 14C the presence of the rest of the bearer member10 is indicated by ghost lines 110.

FIGS. 16 through 18 show an alternative embodiment, in which a slot 120is provided in the domed head 13 c of the bearer 10 and a complementarykey projection 121 is mounted in the boss 42 c of the bearing plate 30c. Operation of the embodiment of FIGS. 16 through 18 is similar to theoperation of the embodiment of FIGS. 13 through 15, except the key 121is provided in the bearing plate 30 c and the slot 120 is provided inthe head 13 c.

FIGS. 19 and 20 illustrate yet a further way in which the bearer member10 may engage with the bearing plate. In this embodiment, the domed head13 d of the bearer member 10 is provided with a plurality of keysurfaces 150. The key surfaces 150 have edges 151 that define boundariesbetween each key surface 150. Complementary receiving key surfaces 152with edges 153 are provided in the receiving boss 42 d of the bearingplate 30 d.

In operation the key surfaces 150 of the head 13 d engage withcomplementary key surfaces 152 of the boss 42 d, preventing relativerotation between the bearer member 10 and the bearing plate 30 d.

FIGS. 21 and 22 show yet a further embodiment which utilises keysurfaces 160 and edges 161 on the head 13 c. These key surfaces 160 aresimilar in operation to the key surfaces of FIG. 19, but there are lessof them. Complementary key surfaces are provided on the boss 42 e of thebearing plate 30 e. They comprise complementary surfaces 163 and edges164.

As well as the above embodiments, there may be other arrangements whichfacilitate engagement of the domed head of the bearer member 10 with thebearing plate so that the bearing member does not rotate, and the cableis not twisted. For example, the embodiments of FIGS. 13 through 18 showonly one key in slot arrangement. There may be two key in slotarrangements on opposite sides of the domed surface/bearing plate boss,or more than two.

Arrangements causing interference between the head and bearing platecould even be used in rock bolt tensioning assemblies that vary from theembodiments described with reference to FIGS. 1 to 10. In fact, any rockbolt tensioning assembly which requires interaction between a head of atensioning component and a bearing plate may utilise any of thesearrangements.

A further embodiment of the tensioning device 1 is disclosed in FIG. 23where the base member 5 does not include a stem portion but merelyincludes the barrel 7 and wedges 6 which clamp that member to the cable3 as described above. To restrict rotational movement of the bearermember 10 relative to the cable, but still allow longitudinal movement(in a manner akin to that provided by keying of the bearer member 10 tostem 8 in the earlier embodiments), a “flower” insert 40 is provided inthe cavity 35 which is contoured to receive the individual stands of therock bolt shaft 3. In this way the bearer member 10 engages directlywith the cable shaft rather than engages the base member 5 as in theearlier embodiment. The arrangement of FIG. 23 is not as preferred asthe earlier arrangements, as the bearer member 10 is not able to movesolely in the longitudinal direction of the shaft as it must follow theline of the individual strands which are helically wound along thelength of the strand. Moreover, the bearer member is not isolated fromthe cable as occurs in the earlier arrangements by the presence of thestem 7 and as such there is some chance that the cable will twist undertensioning. Nonetheless the engagement of the bearer member with thecable does provide some resistance to inhibit twisting of the cableunder tensioning.

In any of the forms described above, the actuator 16 is arranged toreceive the body 11 of the bearer member 10 and extend partially overthe base member 5. The actuator 16 is internally threaded so as toengage with the externally threaded body 11 of the bearer member 10 andincludes a shoulder 17 which is adapted to engage with the shoulder 31formed on the base member 5 at the junction between the barrel part 7and the stem 8 (if present). In this way, the actuator engages both thebase member (through abutment of the shoulders 17 and 31) and the bearermember 10 (through engagement of the cooperating threads on thosemembers).

Rotation of the actuator in one direction (in the illustrated form beingright hand or clockwise looking along the rock bolt from the proximalend 3 b) allows for tensioning of the rock bolt. The actuator 16 isadapted to engage with a drive to impart this rotation with the actuatorbeing shaped so as to engage a drive coupling (dolly) to transmit thatrotational force.

The actuator is provided with an end profile 20 on the actuator end 19that engages in end to end relation with a specially shaped end drive ondolly 200 (see FIGS. 27 to 32), which is described in more detail below.That end profile is best shown in FIGS. 24 to 26.

The end profile 20 on the actuator 16 is shaped generally as a wave ortoothed profile having alternating peaks 43 and troughs 44. The profileincludes a base portion 45 that is of generally constant radius andopposing side walls 46 and 47. One wall 46 is sloped relative to thelongitudinal axis of the actuator 16 and provides a lead in surface forthe complementary teeth 231 of the dolly 200 to locate in the profiletroughs 44, whereas the other wall 47 is disposed in the direction ofthe actuator axis and forms the abutment surface for the actuatorprofile that engages with the dolly drive to impart rotation.

Installation Procedure

In a first stage as disclosed in FIGS. 27 and 28 a rock bolt 2 isinserted into a bore 501 formed in rock strata 500. Fitted to the rockbolt 2 is a bearing plate 30 and a rock bolt tensioning device 1 whichis disposed adjacent a proximal end 3 b of the rock bolt which projectsbeyond the bore 502. At this stage the rock bolt 2 is not point anchoredin the bore 502 but resin cartridges and/or a mechanical anchor areinstalled in conjunction with the rock bolt adjacent the blind end (notshown) of the bore. To activate point anchoring (by shredding and mixingof the resin cartridges and/or activation of a mechanical anchor) therock bolt 2 needs to be spun typically under right hand rotation.

To effect this rotation the dolly 200 is fitted onto the proximal end 3b of the rock bolt shaft 3 as shown in FIGS. 27 and 28. The dolly 200 isdisposed in a cable drive mode so as to allow the end of the rock boltshaft to be fitted within the holder 220 disposed in the cable driveportion of the dolly 200. As best shown in FIG. 27 the sheath 207 issufficiently retracted so that the drive end 204 of the sheath does notengage the actuator 6 of the tensioning device 1.

The dolly is fitted to a drive apparatus (not shown) such as a miningdrill rig through the shaft 202. The drill rig imparts drive to theshaft 202 which in turn is transferred through to the cable driveportion 207 by virtue of the splines 217, 218 interengaging therebyallowing spinning of the rock bolt 3 to provide point anchoring of therock bolt 2. Typically, thrust is also applied to the rock bolt alongthe axis of the bolt so as to push the rock bolt further into the bore501 moving the plate 30 towards the surface 502 of the rock strata 500.This then places the rock bolt into a position as shown in FIGS. 29 and30 where the cable is point anchored by setting of the resin and/or byactivation of the mechanical anchor.

The second stage commences after point anchoring. In this stage thedolly is moved into a tensioning mode by movement of the sheath forwardrelative to the central drive 205 into the position as illustrated inFIGS. 31 and 32. In that position the sheath 208 moves forward so thatthe teeth of the sheath engage with the actuator whilst the end of thecable remains engaged with the cable drive portion 207. By having thedolly 200 adopt the tensioning mode the cable drive portion 207 becomesdisengaged with the sheath 208 and is therefore not driven by the driveshaft 202 and moreover is able to rotate independently of that driveshaft and the sheath 208 This then allows rotation of the actuator bythe dolly relative to the cable 3.

As best illustrated in FIG. 31, a feature of the engagement between thedolly and the actuator is that the diameter of the dolly is no greaterthan the diameter of the actuator. This has significant advantage inmany mining applications as it allows the dolly to be located in moreconfined situations than would otherwise occur if a conventional dollywhich mounted over the actuator (typically in the form of a nut) wasused. This can be particularly advantageous if a “timber jack” is usedas a stabilizing and guiding mechanism for drilling and installingcables. The timber jack usually incorporates a confined opening throughthe centre section of the jack top head frame. Due to the reduceddiameter of the dolly (as compared to more conventional dollies) it hasbeen found in practice possible to tension the bolt using the dolly 200without requiring removal of the timber jack. This improves both speedof operation and safety in the installation procedure.

Once the dolly 200 is installed in engagement both with the cable shaftand the actuator of the tensioning device, drive is imparted to theactuator whilst holding the cable shaft stationary (by virtue ofengagement of the cable shaft with the cable drive portion). Rotation ofthe actuator causes that actuator 6 to unwind from the bearer member 11,this in turn causes the bearing member to move apart from the basemember 5. Under an initial movement the bearer member movement forcesthe plate 30 into engagement with the rock surface 502. Engagement ofthe rock plate 30 hard against the rock surface 502 prevents furthertravel of the bearer member 6 towards the rock surface and also preventsany twisting of the bearer member by virtue of engagement of the bearermember head 13 with the plate 30.

Continued rotation of the actuator 6 under drive imparted from the dolly200 forces the bearer head to continue to move away from the base memberwhich causes increased loading to be induced on the base member 5 by theactuator which has the effect of pulling the cable 2 from the bore. Thistensioning force applied to the base member is offset by a reactionforce applied by engagement of the plate 30 against the rock surface andcauses the cable to be placed in tension.

Once sufficient tension has been applied to the cable, the dolly 200 isremoved thereby leaving the tensioned cable with the tensioning devicestill affixed in place as best illustrated in FIGS. 35 and 36.

The tensioning device, dolly and installation as described in the aboveforms has the advantage that a rotatable actuator can apply an axialforce to the cable (through the base member) without inducing twistingof the cable. In the particular form illustrated the moving component(the bearer member) is isolated from the cable and moreover the entiretensioning device is inhibited from twisting by virtue of engagement ofthe bearer head against the plate 30. In addition the tensioning deviceis of relatively compact form thereby allowing easy handling on site byuse of the drive dolly installation and tensioning of the rock bolt canbe achieved using a standard drill rig thereby obviating the need forspecialist tensioning drives as has occurred in the prior art. Inaddition the drive dolly is of compact form allowing the dolly to beused in confined spaces often found in mining applications.

In the claims which follow and in the preceding summary, except wherethe context requires otherwise due to express language or necessaryimplication, the word “comprising” is used in the sense of “including”,that is the features specified may be associated with further featuresin various embodiments.

Variations and modifications may be made to the parts previouslydescribed without departing from the spirit or ambit of the disclosure.

1. A tensioning assembly for a rock bolt, the tensioning assemblycomprising an engagement head that in use is forced into either director indirect engagement with a rock surface, wherein the engagement headis profiled to include at least one key surface to inhibit rotation ofthe engagement head relative to the rock surface.
 2. A tensioningassembly according to claim 1, wherein the engagement head is arrangedto engage the rock surface through abutment with a plate-like member andwherein rotation of the engagement head relative to the plate-likemember is inhibited by the at least one key surface.
 3. A tensioningassembly according to claim 2, wherein the at least one key surface isformed as one or more flattened surfaces formed on the engagement head.4. A tensioning assembly according to claim 2, wherein the at least onekey surface comprises one or more lateral surfaces that project radiallyfrom an axis of the engagement head.
 5. A tensioning assembly accordingto claim 4, wherein the one or more lateral surfaces project radiallyfrom a central zone towards the circumference of the engagement head. 6.A tensioning assembly according to claim 2, wherein the at least one keysurface is located on a projection extending outwardly from thecircumference of the head.
 7. A tensioning assembly according to claim2, wherein the at least one key surface is located in a slot extendinginto the head.
 8. A tensioning assembly according to claim 2, whereinthe engagement head forms part of a bearer member incorporating apassage through which the rock bolt extends.
 9. A tensioning assemblyaccording to claim 8, wherein the bearer member includes an innersurface that defines said passage and which incorporates a surface thatcooperates with an abutment mounted to, or formed in, the rock bolt toprovide a positive engagement therebetween that inhibits rotation of thebearer member relative to the abutment about the bolt in at least onedirection.
 10. A combination comprising a tensioning assembly accordingto claim 2 and a plate-like member arranged to directly engage the rocksurface, the plate like member including at least one plate key surfacethat cooperates with the at least one key surface of the engagement headto inhibit rotation therebetween.
 11. An engagement assembly forengagement between a rock surface and a tensioning assembly, theengagement assembly comprising: a plate-like member arranged to directlyengage the rock surface, the plate like member including at least oneplate key surface; and a bearer member arranged to engage with, or formpart of, the tensioning assembly, the bearer member having a headincluding at least one head key surface, wherein the head key surfaceand the plate key surface are adapted to engage such that rotation ofthe head relative to the rock surface is inhibited.
 12. An engagementassembly according to claim 11, wherein the at least one head keysurface is formed as one or more flattened surfaces formed on the bearermember head.
 13. An engagement assembly according to claim 11, whereinthe at least one head key surface comprises one or more lateral surfacesthat project radially from an axis of the bearer member head.
 14. Anengagement assembly according to claim 13, wherein the one or morelateral surfaces project radially from a central zone towards thecircumference of the bearer member.
 15. An engagement assembly accordingto claim 13, wherein the at least one head key surface is located on aprojection extending outwardly from the circumference of the head. 16.An engagement assembly according to claim 13, wherein the at least onehead key surface is located in a slot extending into the head.
 17. Arock bolt assembly comprising a rock bolt having an axis, a bearermember for facing and urging against rock strata, the rock bolt beingarranged to extend through the bearer member, and an abutment mountedto, or formed in the rock bolt, wherein the abutment and the bearermember incorporate cooperating surfaces that provide positive engagementtherebetween that inhibit rotation of the abutment relative to thebearer member about the bolt axis in a least one direction.
 18. A rockbolt assembly according to claim 17, further comprising an engagementassembly according to claim 11, wherein the bearer member forms part ofthe engagement assembly.
 19. A method of inhibiting rotation of atensioning assembly with respect to a rock surface, the tensioningassembly including a bearer member, the method comprising: positioning aplate-like member in contact with the rock surface; positioning a bearermember in contact with the plate like member; and causing a key surfacein the bearer member to abut a corresponding key surface in theplate-like member.